| 摘要 |
PURPOSE:To make it possible to obtain a height signal with high reliability by sampling plural pieces of output signals of an electrostatic capacity type height sensor during diminishing of a laser beam and predicting a convergence value in accordance with a time change thereof. CONSTITUTION:A laser beam waveform signal is supplied to a timing circuit 22 which detects the time of the irradiation with the laser beam and the time of non-irradiation. This timing circuit 22 generates plural times of sampling signals within the prescribed time when the laser beam is diminished by taking the time necessary for noises to diminish at the time of the irradiation with the laser beam. A sampling circuit 23 samples the height sensor measurement signals in accordance with this signal. A convergence value computing circuit 25 calculates the convergence value of the signals by receiving these signals and supplies the height signal. Then, the high reliability and high accuracy are obtd. by utilizing the data of the part gradually changing toward a stationary state. |
